1. Field of the Invention
This invention relates to sputtering equipment for deposition of thin-film materials and, more particularly, to improved shielding for such equipment.
2. Prior Art
Sputtering is a physical process used for the deposition of thin films materials. Sputtering uses the kinetic energy of accelerated ions of an inert gas, such as argon, to transfer energy to the materials of a target. Upon impact by the accelerated ions, molecules of the target material are dislodged from the surface of a target. The dislodged molecules form a vapor which is then deposited on a desired substrate. Sputtering processes are used to deposit thin films of a variety of sputtered materials on a variety of surfaces. Sputtering is often used where thin-film chemical-vapor deposition (CVD) cannot be used, such as, for example, for depositing refractory materials.
FIG. 1 illustrates a prior art sputter source 10. The sputter source 10 typically is one station of a multi-station assembly for performing various processing steps on a semiconductor wafer. At each station a specific processing function is performed. For example, the sputter source 10 provides a source of Ti/W material to be deposited on the surface of a wafer. Each of the stations is arranged in a circular pattern on a large rear mounting plate 12. The wafers are mounted to carriers which are rotated, or stepped, to the various stations on the mounting plate 12.
The sputter source 10 includes an anode 13 and a ring-shaped Ti/W cathode, or target, 14. Energized argon ions bombard the surface of the cathode 14 to continuously generates a cloud of ions of sputtered Ti/W material. The sputtered Ti/W ions are contained close to the sputter source 10 by a movable shutter 16. The movable shutter 16 is mounted to a shaft 18, which is rotatably mounted to the rear plate 12. A wafer is positioned adjacent to the shutter 16 and the shutter 16 is rotated to expose the wafer to ions from the sputter source 10 for a predetermined time to form a film of sputtered material on the exposed surface of the wafer.
The anode 13 and the cathode target-ring 14 are mounted to a cylindrical weldment, or mounting structure 20, which extends perpendicularly from the rear mounting plate 12. Mounted to the distal end of the cylindrical mounting structure 20 is a water-cooled cooling ring 22. A baffle shield member has an outer flat ring-shaped base portion 24, which overlies the water-cooled cooling ring 22. From the flat ring-shaped base portion 24 extends a baffle portion 26, which extends inwardly and which provides a barrier for sputtered material. The flat ring-shaped base portion 24 of the baffle shield is fixed to the distal end of the cylindrical mounting structure 20 with a number of bolts, typically shown as 28.
A front shield assembly 30 includes a cylindrical front shield 32 which is attached to a flat annular disk member 34. The cylindrical front shield 32 surrounds the outside surface of the end of the cylindrical mounting structure 20. The disk member 34 projects over the flat ring-shaped base portion 24 of the baffle shield. The front shield assembly 30 is fixed to the cylindrical mounting structure with screws (typically shown as 36).
A space, or gap, 40 is formed between the base 24 and the disk member 34. The heads of the bolts 28 are contained within the gap 40. One problem with this prior art sputter source is that the space, or gap, 40 formed between the base 24 and the disk member 34 permits sputtered material in a powdery form to be deposited on the surfaces within the gap. Sputtered material is also deposited on the base of the cylindrical mounting structure, which is not covered by a shield. This powdery material flakes off and contaminates the surface of a wafer being sputter-coated.
FIG. 2 shows that the inner lip 42 of the annular disk member 34 forms a flat, squared edge with sharp corners. Sputtered material is deposited on the inner sharp corner of the lip 42 and forms a deposit 44 as indicated in the Figure. Ti/W material is brittle and as the front shield is heated and cooled, the sputtered material such as Ti/W, on the sharp corner of the lip of the front shield flakes away to also contaminate the surface of a wafer being processed.
Consequently, the need has arisen for a shielding arrangement which reduces flaking of deposited sputtered material from the base of the cylindrical mounting structure and from the gap between the base 24 of the baffle shield member and the disk member 34.